The Tektronix CG5001 is a programmable calibration generator plug-in for the TM5000 system.

The 1983 Tektronix Catalog, on page 379, says:

The CG5001 requires either a TM5003 or TM5006. The CG551AP is a TM500 version of the CG5001 and requires a TM506 Mod JB, TM515 Mod UB, or RTM506 Mod JB. The CG5001 is not compatible with TM500 power module mainframes.